Micro liquid crystal displays having a circular cover glass and a viewing area free of spacers

ABSTRACT

The invention relates to liquid crystal displays and method of making liquid crystal displays. One liquid crystal display invention has as an element an optically transmissive first substrate that may be positioned to receive light incident from the light source. A reflective second substrate is positioned adjacent to this first substrate. The second substrate has an active area that may include a circuit panel and a perimeter seal area surrounding that active area. To separate the first substrate from the second substrate, spacers are configured about the perimeter seal area of the second substrate. Between the first substrate and the second substrate is a liquid crystal material. Other embodiments are disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates micro liquid crystal displays that use digital andreflective technology. The invention may be used to produce high qualitystatic as well as dynamic real time color field micro images on anactive pixel matrix.

2. Background Information

Conventional flat-panel displays use electroluminescent materials orliquid crystals in conjunction with incident light to produce highquality images in products such as digital wristwatches, calculators,panel meters, thermometers, and industrial products. Liquid crystals area state of matter that mixes the droplet or pouring property of a liquidand the long-range order property of a solid. This combination allows anoptical activity having a magnitude without parallel in either solids orliquids. Further, when a magnetic or electrical field is applied normalto the liquid crystal material, the liquid crystal material forms alocalized monocrystal that is polar in character. This localizedpolarization of the liquid crystal material affects the travel path oflight incident to the liquid crystal material. By controlling theelectrical field applied across the liquid crystal material, the travelpath of light incident to the liquid crystal material can be controlledto help produce high quality images.

Modern approaches for developing high quality liquid crystal displays(LCDs), also referred to as liquid crystal spatial light modulators(SLMs), utilize an active-matrix approach where thin-film transistors(TFTs) are operationally co-located with a matrix of LCD pixels. Theactive-matrix approach using TFT-compatible LCDs eliminates cross-talkbetween pixels to allow finer gray scales. For example, see U.S. Pat.No. 5,767,828 entitled Method and Apparatus for Displaying Grey-Scale orColor Images from Binary Images and invented by an inventor of the belowdisclosed invention.

Flat-panel displays employing LCD panels generally include fivedifferent layers: A white light source, a first polarizing filter thatis mounted on one side of a circuit panel on which the TFTs areassembled in arrays to form pixels, a filter plate containing at leastthree primary colors arranged into pixels, and a second polarizingfilter. A volume between the circuit panel and the filter plate isfilled with a liquid crystal material. U.S. Pat. No. 5,868,951 entitledElectro-Optical Device and Method and co-invented by an inventor of thebelow disclosed invention relates to flat-panel displays.

Nematic liquid crystal material is frequently used in LCDs since itsproperties are well understood and it is easy to align. This materialwill not rotate polarized light when an electric field is applied acrossit between the circuit panel and a ground affixed to the filter plate.The first polarizing filter generally converts the incident light intolinearly polarized light. When a particular pixel of the display isturned on, the liquid crystal material rotates the polarized light beingtransmitted through the material. Thus, light passes through the filterplate and is detected by the second polarizing filter.

Conventional liquid crystal displays such as amorphous TFT andsuper-twist nematic (STN) displays employ large external drivecircuitry. However, the amorphous silicon transistors of conventionalliquid crystal displays lack the electron mobility and leakage currentcharacteristics necessary for micro liquid crystal displays. Moreover,size and cost restraints for micro liquid crystal displays generallyrequire the drive circuitry of an integrated circuit to be integratedinto the display along with the pixel transistors. Because the drivecircuitry must be fabricated on the display substrate, micro displaysare generally limited to high quality transistor technology such assingle crystal (x-Si) and polysilicon (p-Si).

Micro display technologies can roughly be divided into two types:transmissive and reflective. Transmissive micro displays includepolysilicon TFT displays. Polysilicon TFT displays dominate displaytechnology in high-end projection systems and are also used asviewfinder displays in hand-held video cameras. They are usually basedon twisted nematic (TN) construction. See U.S. Pat. No. 5,327,269entitled Fast Switching 270 Degree Twisted Nematic Liquid Crystal Deviceand Eyewear Incorporating the Device and invented by an inventor of thebelow described invention.

The aperture ratio of a transmissive micro display is obtained bydividing the transmissive area by the total pixel area. High resolutionpolysilicon displays such as Super Video Graphics Array (SVGA) arelimited to what is considered larger micro displays having 0.9-1.8 inchdiagonal (22.9-45.7 millimeter diagonal). This is because the arearequired by the pixel transistors and the addressing lines reduces theaperture ratio. Aperture ratios for polysilicon displays are usuallyaround 50%. Single crystal silicon transmissive displays are similar topolysilicon TFT displays but use a transistor lift-off process to obtainsingle crystal silicon transistors on a transparent substrate.

Reflective micro displays are usually based on single-crystal siliconintegrated circuit substrates with a reflective aluminum pixel forming apixel mirror. Because it is reflective, the pixel mirror can befabricated over the pixel transistors and addressing lines. This resultsin an aperture ratio (reflective area/absorptive area) that is muchlarger than polysilicon displays. Aperture ratios for reflectivedisplays can be greater than 90%. Because of the large aperture ratioand the high quality silicon transistors, the resolution of a reflectivemicro display can be very high within a viewing area that is quitesmall.

There are several different liquid crystal technologies currently usedin reflective micro displays. These include ferroelectric liquid crystal(FLC), polymer disbursed liquid crystal (PDLC), and nematic liquidcrystal. Size and resolution of reflective micro displays may range from0.25 inch diagonal (QVGA) to 0.9 inch diagonal (SXGA) (6.4-22.9millimeter diagonal). Reflective micro displays are limited in physicalsize because as the size increases the cost increases and yielddecreases.

For further background in this area, see Douglas J. McKnight, et al.,256×256 Liquid-Crystal-on-Silicon Spatial Light Modulator, 33 AppliedOptics No. 14 at 2775-2784 (May 10, 1994); and Douglas J. McKnight etal., Development of a Spatial Light Modulator: A Randomly AddressedLiquid-Crystal-Over-Nmos Array, 28 Applied Optics No. 22 (November1989).

SUMMARY OF THE INVENTION

The invention relates to liquid crystal displays and method of makingliquid crystal displays. One liquid crystal display invention has as anelement an optically transmissive first substrate that may be positionedto receive light incident from the light source. A reflective secondsubstrate is positioned adjacent to this first substrate. The secondsubstrate has an active area that may include a circuit panel and aperimeter seal area surrounding that active area. To separate the firstsubstrate from the second substrate, spacers are configured about theperimeter seal area of the second substrate. Between the first substrateand the second substrate is a liquid crystal material. Other embodimentsare disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a planar side view of an optically transmissive substrateand a semiconductor substrate or wafer;

FIG. 2 is a perspective top view of the substrates of FIG. 1;

FIG. 3 is a planar side view of the substrate and wafer after thesubsequent processing step of depositing a conductive coating on anoptically transmissive substrate;

FIG. 4 shows the subsequent processing step of depositing alignmentlayers on one surface of the substrate and the wafer;

FIG. 5 schematically illustrates an apparatus for rubbing the surface ofthe alignment layers with a velvet cloth;

FIG. 5 shows a cylinder having a velvet cloth on its surface;

FIG. 6 shows exemplary rub directions for opposing alignment layers of asubstrate and a wafer 115;

FIG. 7 schematically illustrates a planar top view of a wafer includinga plurality of micro display areas;

FIG. 8 illustrates one micro display area of the semiconductor wafer;

FIG. 9 shows a cross section of a display area taken through line A—A ofFIG. 8;

FIG. 10 shows the wafer after the deposition of cross-over material;

FIG. 11 shows an optically transmissive substrate and a wafer assembledtogether in a mechanical press;

FIG. 12 shows that a shim plate is flexible enough to conform to thepresence of foreign particles;

FIG. 13 illustrates the cross-over material piercing the alignmentlayers;

FIG. 14 illustrates the use of a conformal bag press;

FIG. 15 illustrates how the gap may also be used as an entrance forliquid crystal display material;

FIG. 16 shows the optically transmissive substrate/wafer assemblylowered into a liquid crystal material bath;

FIG. 17 shows liquid crystal material forced into the cell gap due topressure differential;

FIG. 18 illustrates a compensating or retarder film laminated to theentire surface of the transmissive substrate;

FIG. 19 shows the street areas between the individual display devices;

FIG. 20 shows the case where the transmissive substrate is square;

FIG. 21 illustrates how the semiconductor wafer is diced from thebackside;

FIG. 22 shows the backside of the wafer after the step of partialcutting of all of the semiconductor wafer;

FIG. 23 shows the assembly after the scribing of the glass material inan X-direction;

FIG. 24 shows the assembly after the scribing of the glass material in aY-direction;

FIG. 25 shows a top view of the assembly with the pattern-side of waferfacing in the up position;

FIG. 26 shows an embodiment where the perimeter of the transmissivesubstrate follows the generally round perimeter of the wafer;

FIG. 27 shows material removed from the wafer to provide X- andY-registration;

FIG. 28 shows the individual display assemblies from an x-direction;

FIG. 29 shows the same assemblies from y-direction;

FIG. 30 shows a singulated device put in a vacuum chamber;

FIG. 31 shows liquid crystal material forced into the display area dueto pressure differential;

FIG. 32 shows a singulated device position with the fill port facing upwithin a chamber;

FIG. 33 illustrates the chamber in the pressurized state;

FIG. 34 illustrates a cross-section of an individual display from anX-direction;

FIG. 35 illustrates a cross-section of an individual display from anY-direction;

FIG. 36 shows the micro liquid crystal display ready to be packaged intoa micro liquid crystal display panel;

FIG. 37 shows a single-chip radio manufactured by Lucent TechnologiesInc.;

FIG. 38 illustrates a size comparison between a U.S. penny, aconventional ceramic filter, and a miniature RF filter; and

FIG. 39 shows a tank circuit having a miniature inductor and capacitor.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are set forthsuch as specific materials, processing steps, processing parameters,etc., in order to provide a thorough understanding of the invention. Oneskilled in the art will recognize that these details need not bespecifically adhered to practice the claimed invention. In otherinstances, well known processing steps, materials, etc., are not setforth in order not to obscure the invention. As indicated under MPEP2164.01, a patent need not teach, and preferably omits, what is wellknown in the art.

The following describes an embodiment of forming a liquid crystaldisplay, cell, or device, in accordance with the invention. FIG. 1 showsa planar side view of optically transmissive substrate 100 andsemiconductor substrate or wafer 115. In this embodiment, the characterof substrate 100 is optically transmissive where optically transmissivesubstrate 100 may serve as a cover that is positioned to receive lightincident from a light source (not shown). Moreover, opticallytransmissive substrate 100 may be approximately 1.1 millimeters (mm)thick. Optically transmissive substrate 100 may include cover glassmaterial 102, such as Corning 1737 industrial grade boroaluminosilicateglass available from Applied Films Corporation of Boulder, Colo. Withthe processing temperature ranges for making liquid crystal displaysbeing between 0 degrees Celsius (degs. C.) and 300 degs. C., Corning1737 is a preferable glass material because it is readily availabilityand its coefficient of thermal expansion (Corning 1737CTE=37.6×10⁻⁷/deg. C.) is very close to that of silicon. In thisembodiment, optically transmissive substrate 100 may include a film ofretarder layer 110 laminated to glass material 102 as seen in FIG. 1 andFIG. 18. Retarder layer 110 serves to compensate for residualbirefringence in liquid crystal during the “on” (black) state. Retarderlayer 110 improves the contrast of the display.

FIG. 1 also shows semiconductor wafer 115 that contains, for example, aplurality of flat-panel display circuitry. The circuitry preferably isbased on single-crystal silicon integrated circuit substrate technologywith a reflective pixel layer. In the embodiment shown, the individualdisplay circuitry of wafer 115 is, for example, reflection modecircuitry. This reflection is illustrated in FIG. 1 by reflective pixellayer 125. Reflective pixel layer 125 is fabricated preferably out ofaluminum over the mode circuitry having pixel transistors and addressinglines within backplane 120 of wafer 115. In this embodiment, thealuminum provides a reflective character to pixel layer 125. Othermaterials such as gold or silver that are capable of reflectingsufficient undiffused light to form a virtual image so as to faithfullyreflect or give a true picture may be used. It is to be appreciated thatthe invention is not limited to semiconductor wafer arrays. Othersubstrate arrays such as, for example, silicon on insulator (SOI)arrays, can also be used to form the individual display devices of theinvention.

FIG. 2 is a perspective top view of the substrates of FIG. 1. FIG. 2shows cover glass 102 situated above circuitry pattern-side 117 ofsemiconductor wafer 115. Wafer 115 is shown with reflective pixel layer125 over a plurality of reflection mode display circuitry revealed onpattern-side 117 of backplane 120.

FIG. 3 is a planar side view of substrate 100 and wafer 115 after thesubsequent processing step of depositing conductive coating 130 onoptically transmissive substrate 100. In one embodiment, opticallytransmissive substrate 100 is glass material 102 made of Corning 1737glass having conductive coating 130 of Indium-Tin-Oxide (ITO) applied toone side. ITO is a transparent metal oxide coating that may be depositedon glass material 102 by way of a sputtering operation. ITO is anindustry standard conductive film because of its high opticaltransmission and low electrical resistance. ITO preferably is applied tothe Corning 1737 glass at a coating thickness of 190 angstroms (Å)nominal. At 190 angstroms (Å), conductive coating 130 exhibits a sheetresistance of 60 ohms/square minimum to 125 ohms/square maximum and atransmission of 84% minimum at 550 nanometers (nm). U.S. Pat. Nos.5,230,771, 5,171,401, and 5,032,221 were co-invented by an inventor ofthis patent and relate to plasma etching of Indium Tin Oxide.

In this embodiment, conductive coating 130, such as ITO layer, is notpatterned. It has been found that depositing conductive coating 130without patterning, simplifies the manufacturing process because iteliminates the need for photolithography processing. Importantly,un-patterned cover glass substrate 100 also simplifies the assemblyprocess because it allows for a simple mechanical alignment of substrate100 and wafer 115 rather than a more complicated camera-assistedalignment as is conventionally employed.

FIG. 4 shows the subsequent processing step of depositing alignmentlayers 135 on one surface of optically transmissive substrate 100 and ona complementary surface of semiconductor wafer 115. In one embodiment,alignment layer 135 is a polyimide material manufactured by NissanChemical Industries of Tokyo, Japan. Polyimide is an industry standardmaterial for nematic liquid crystal alignment layers because of its easyof application, its excellent anchoring of liquid crystal molecules, andits support of a wide range of pre-tilt angles. In one embodiment,alignment layer 135 is NISSAN SE-7492™ polyimide material purchased as asolution to be spin-coated on substrate 100 and substrate 115. In thisembodiment, the polyimide initially has a 6% solids content. Prior todeposition onto optically transmissive substrate 100, the polyimide isdiluted with Nissan Solvent 21 (or Nissan Solvent 2M) to a 2% solidsolution. NISSAN SE-7210™ may also be used for alignment layer 135.

In the application of alignment layer 135, optically transmissivesubstrate 100 and semiconductor wafer substrate 115 are spun-coated witha 2% solids polyimide solution. Spin coating is a method of filmdeposition that provides a uniform coating across the surface of thesubstrate. Spin coating equipment is widely used in the displayprocessing industries.

After substrate 100 and wafer 115 are coated with alignment layers 135,the polyimides of alignment layers 135 are cured. The substrates firstreceive a low temperature soft bake (e.g., 100 deg. C. on metal surfacein convection oven) to remove the solvents, then a high temperature hardbake (e.g., ramp from 100 deg. C. to 180 deg. C. in 10 minutes; totalhard bake cycle time 60 minutes) to fully cure the polyimide. The cureprocesses of the invention preferably are performed in a clean roomconvection oven.

One purpose of alignment layers 135 is to establish the opticalreference axis of the liquid crystal material. Once alignment layers 135are deposited and cured on substrate 100 and wafer 115, alignment layers135 may be aligned in accordance with the desired light rotation of theliquid crystal material molecules that will form part of the individualdisplay. The alignment direction of the liquid crystal molecules isobtained by means of rubbing the exposed surface of alignment layers 135with a velvet cloth.

FIG. 5 schematically illustrates apparatus 148 for rubbing the surfaceof alignment layer 135 with velvet cloth 145. As a soft fabric, such assilk, rayon, or nylon, velvet is preferred to impart the alignmentdirection because of its smooth, dense pile and a plain underside. FIG.5 shows a cylinder 142 having velvet cloth 145 on its surface. Cylinder142 rotates, in this case, in a clockwise direction. Substrate 100 or115 having alignment layer 135 rests on a horizontally moving stage 140so that alignment layer 135 of substrate 100 or 115 comes in contactwith velvet cloth 145 of cylinder 142. In one embodiment, cylinder 142rotates at a speed of 400 revolutions per minute and has a motor drag of37 millivolts. Stage 140 moves in a horizontal direction at a speed ofapproximately 0.75 inches per second yielding a table stage motion axisrelative to cylinder rotation axis of 90 degrees and rub depth of 0.020inches. A suitable material for cloth 145 may be, for example, theYA-20-R rayon cloth produced by Yoshikawa Chemical Company of Tokyo,Japan.

FIG. 6 shows exemplary rub directions for opposing alignment layers 135of substrate 100 and wafer 115 as imparted via apparatus 148 of FIG. 5.It is to be appreciated that the depth and direction of the rub is afunction of, for example, the liquid crystal molecules chosen for theindividual display. The above description of the rub process ofalignment layers 135 is presented in detail herein by way of explanationand not by way of limitation, in accordance with the description of theparticular liquid crystal display described herein.

Once alignment layers 135 are deposited on substrate 100 and 115 and rubdirections are established on alignment layers 135, spacers are appliedto semiconductor wafer 115. As described in connection with FIG. 7, onepurpose of applying spacers is to create cell gap 207 (FIG. 11) for theplacement of liquid crystal molecules between substrate 100 andsubstrate 115.

In most prior art display applications, spacers are dispersed randomlyacross the entire display substrate, including the viewing area. Inlarge area displays, for example, the spacers in the viewing areamaintain spacing uniformity because large glass substrates overlyingdisplay circuitry can warp. Spacers in the viewing area of a display areundesirable since they can reduce the contrast of the display by notrotating the localized incoming light from a white light source.

FIG. 7 schematically illustrates a planar top view of wafer 115including a plurality of micro display areas 155. In one embodiment,there are 86 micro display areas 155. FIG. 7 shows a perimeter sealmaterial 150 containing spacers 152 (FIG. 8) surrounding the perimeterof each of a plurality of display area 155 as well as surrounding theinside perimeter of wafer 115. Perimeter seal material 150 may be athermal cure adhesive as discussed below and spacers 152 may be silicaspheres.

Material 150 preferably comprises white silica spheres initially in adry state. To form perimeter seal material 150, this dry spacer materialis first mixed with a solvent, for example the solvent known as “DEC”,in a concentration of approximately 0.072 grams spacer material to 1.0gram DEC. The materials are mixed in a container. The mixture is thenplaced in an ultrasonic bath for fifteen minutes to thoroughly mix theparticles in the solvent and to break up any clumps of material. Thesolvent and spacer mixture is then mixed with 20 grams of perimeter sealmaterial. In this embodiment, perimeter seal material 150 is aheat-cured adhesive. It is to be appreciated that there are manysuitable adhesives including, but not limited to, heat- andultraviolet-cured adhesives.

Perimeter seal material 150 containing spacers 152 may be applied usinga syringe having a fluid dispensing system, such as one manufactured byAsymtek of Carlsbad, Calif. An automatic dispensing system may consistof a syringe mounted above wafer substrate 115 having full X- andY-motion capabilities. Perimeter seal material 150 including spacers 152may then be dispensed from a needle, for example a 0.006 inch insidediameter lavender needle, and the flow of material may be controlledpneumatically, for example at a dispensing speed of 0.28 inches persecond and a dispensing pressure of 24 pounds per square inch with aneedle height of 0.003 inches. In this manner, a consistent 0.5millimeter perimeter seal line width is obtained for perimeter seal area165.

Perimeter seal material 150 containing spacers 152 is dispensed in theperimeter seal areas 165 as shown in FIG. 8. As shown in FIG. 7, apattern (perimeter seal material 150 encapsulating spacers 152) is alsodispensed at the edge of wafer 115 in the “unused” areas of wafer 115.This additional edge pattern is a support structure that works toprevent wafer 115 from collapsing at its edges. Without this supportstructure around the edge of wafer 115, wafer 115 cannot adequatelysupport the force required to press together wafer 115 and opticallytransmissive substrate 100. Without sufficient press force, anon-uniform cell gap 207 that is collapsed at the edge of wafer 115 willbe formed. The perimeter seal around the outer edge of wafer 115 alsoworks as a seal to prevent water from entering the cell gap during awafer dicing process.

The next step in forming a LCD display in accordance with an embodimentof the invention is the deposition of a cross-over material on eachdisplay area 155 of wafer 115. Recall that when a magnetic or electricalfield is applied normal to the liquid crystal material, the liquidcrystal material forms a localized monocrystal that is polar incharacter. A cross-over may be thought of as an adhesive material orepoxy into which conductive material is disbursed so as to aid increating an electrical path between the reflection mode displaycircuitry that resides below the reflective pixel layer of the wafer andthe conductive coating layer attached to the glass cover. In otherwords, cross-over material 170 communicates the cover glass drivevoltage from reflective pixel layer 125 of wafer 115 to conductivecoating 130 of substrate 100. Conventionally, the cross-over material ismade of silver particles or gold-coated plastic particles.

To conventionally create this electrical path, alignment layers 135 arefirst removed or etched away to create a path in reflective pixel layer125 and in conductive coating 130. Then, the cross-over material isadhered to this path in reflective pixel layer 125 and brought intocontact with the path in conductive coating 130. Alternatively, aspecial mask conventionally is created to mask off the cross-over pathsprior to applying the polyimide.

In an embodiment of the invention, cross-over material 170 preferablycontains particles made of conductive nickel. The nickel particlessurprisingly permit cross-over material 170 to break through thepolyimide alignment layers 135 to create the desired electrical path.Thus, the use of nickel particles eliminates the need to etch awayalignment layers 135 or use a mask prior to applying alignment layers135.

To form an embodiment of cross-over material 170, nickel particleshaving 2.0 micron nominal diameters are first mixed with a solvent, forexample DEC, in a concentration of approximately 0.669 grams ofcross-over material to 1.0 grams of DEC. The materials are mixed in acontainer and sealed. The mixture is then placed in an ultrasonic bathfor fifteen minutes to thoroughly mix the particles in the solvent andto break up any clumps of material. The solvent and nickel particlemixture is then mixed with 20 grams of perimeter seal material. Similarto perimeter seal material 150, an Asymtek fluid dispensing machine maybe used to dispense cross-over material 170. In one embodiment, themachine includes a dispensing needle size of approximately 0.006 inchesinside diameter, a needle height of 0.002 inches, and a dispensingpressure of 24 pounds per square inch.

Once cross-over material 170 is placed on the individual display area155 of wafer 115, wafer 115 and optically transmissive substrate 100 areassembled together. In one embodiment, wafer 115 is placed on a metalsurface in a pre-heated convection oven and baked at 40 deg. C. forapproximately seven minutes as a pre-cure. This pre-cure bake evaporatessolvents, for example the DEC solvent, in perimeter seal material 150.Wafer 115 is then placed on a hot plate at 75 deg. C. Wafer 115 isallowed to reach the heated temperature, then optically transmissivesubstrate 100 is placed over wafer 115 and tacked onto wafer 115.

FIG. 8 illustrates one micro display area 155 of semiconductor wafer115. Display area 155 may include a viewing area 160 and a perimeterseal area 165. Perimeter seal area 165 includes a plurality of spacers152 in perimeter seal adhesive 150. FIG. 8 shows that the spacers 152and perimeter seal adhesive 150 are disbursed generally throughoutperimeter seal area 165. One exception is fill port area 167 ofperimeter seal area 165. Area 167 is left free of perimeter sealmaterial 150 and spacers 152 to allow a path for the placement of liquidcrystal display material (material 220, FIG. 16; material 310, FIG. 30;and material 311, FIG. 32) into display area 160. As shown in FIG. 10,the matrix of spacers 152 may include more than one spacer 12 acrossarea 165.

Spacers 152 such as shown in FIG. 8 are added to perimeter seal area 165to create cell gap 207 (FIG. 11) between wafer 115 and opticallytransmissive substrate 100. Cell gap 207 is created to permit placementof liquid crystal material between wafer 115 and optically transmissivesubstrate 100. Perimeter seal material 150 seals the gap between wafer115 and substrate 100 along the pattern of perimeter seal area 165 tocapture liquid crystal material within each viewing area 160. Similar tofill port area 167 of FIG. 8, gap 153 of FIG. 7 is left free ofperimeter seal material 150 and spacers 152. This permits trapped air toescape as wafer 115 is affixed to optically transmissive substrate 100.Gap 153 may also be used as an entrance for liquid crystal displaymaterial 220 (FIG. 15).

FIG. 9 shows a cross section of display area 155 taken through line A—Aof FIG. 8. FIG. 9 shows display area 155, display area 160, perimeterseal area 165, cross-over material 170, and spacers 152. The outsidediameter of spacers 152 is a function of the desired thickness of theliquid crystal material layer, such as cell gap 207 of FIG. 11. In oneembodiment, spacers 152 may be 2.1 micron silica spheres from BangsLaboratories of Fishers, Ind. Spacers having an outside diameter rangingfrom 1.5-3.0 microns are used in this embodiment. Spacers 152 are mixedwith perimeter seal material where the mixture is applied to perimeterseal area 165 of display area 155 of wafer 115 and to the insideperimeter of wafer 115 (FIG. 7) during a perimeter seal applicationprocess.

As noted above, gap 153 of FIG. 7 is left in the wafer perimeter seal toallow air to escape during a subsequent press and cure process. Gap 153also permits the positioning of liquid crystal material between wafer115 and optically transmissive substrate 100 prior to dicing or“singulating” wafer substrate 115. Gap 153 is later filled with anadhesive to complete display area 160.

FIG. 10 shows wafer 115 after the deposition of cross-over material 170.Cross-over material 170 provides, in one manner, electrical contactbetween wafer 115 and optically transmissive substrate 100, such as seenin FIG. 34 and FIG. 35. In the embodiment where spacers 152 have anoutside diameter of 2.1 microns, cross-over material 170 preferablycontains 2.0 micron nominal diameter nickel particles purchased fromGoodfellow, Inc. of Cambridge, England. Other conductive particles areacceptable substitutes for nickel where supplied in a particle formhaving similar conductive characteristics and break-throughcharacteristics as nickel. In this embodiment, because conductivecoating 130 of transmissive substrate 100 has no patterning, amechanical alignment method can be used during assembly as shown in FIG.10.

Once optically transmissive substrate 100 and wafer 115 are assembledtogether, the substrates may be placed in mechanical press 180 as shownin FIG. 11. Mechanical press 180 consists of two heated aluminum plates185 and 187 hinged together in a clamshell fashion wherein each shell isparallel to one another. In this embodiment, bottom plate 187 includesan inflatable bladder 195. Inflatable bladder 195 provides the directpressure required to assemble together transmissive substrate 100 andwafer 115.

In one embodiment, a clean 1.1 millimeter thick borosilicate glass shimplate 200 having approximately the same or larger surface area asoptically transmissive substrate 100, for example, a 7-inch squaresurface area, is placed over bladder 195 of bottom plate 187. Wafer 115and optically transmissive substrate 100 are thoroughly cleaned. Firstwafer 115 and then substrate 100 each are stacked on glass shim plate200. Pressure is then applied to wafer 115 and transmissive substrate100 by inflating the bladder against glass shim plate 200. The inflatingbladder 195 as restricted by plate 185 and plate 187 forces wafer 115and transmissive substrate 100 together. Wafer 115 and substrate 100 arepressed together in such a manner that cross-over material 170 pierceseach alignment layer 135 to make contact between conductive coating 130and reflective pixel layer 125 as seen in FIG. 13. In one embodiment,wafer 115 and substrate 100 are pressed together so that they areseparated by a distance of approximately 2 microns at cell gap 207.

As shown in FIG. 11, optically transmissive substrate 100 has a largersurface area than semiconductor wafer 115, for example, seven-inchsquare optically transmissive substrate 100 versus six-inch diameterwafer 115. To prevent glass shim plate 200 from flexing at assembly edge202 when bladder 195 is inflated, shims 205, for example glass shims, ofthe same thickness as wafer 115 are placed at the periphery of wafer 115on plate 200.

The retaining method of combining glass shim plate 200 with inflatablebladder 195 and shims 205 results in a uniform cell gap 207 across theassembly, between transmissive substrate and wafer 115. The uniform cellgap 207 across the assembly is better than that which would be achievedusing only hard plates or an inflatable bladder without a glass shimplate or shims.

Glass shim plate 200 acts as a semi-rigid, two-dimensional support beamdistributing the pressure applied by bladder 195 only to areas wherespherical spacers 152 are present between substrate 100 and wafer 115.Because spacers 152 are present only in perimeter seal areas 165, thepressure applied by the mechanical press is applied primarily to theseals and not to the interior, e.g., cell gap 207, of individual displaydevices. The application of pressure only to the seals prevents wafer115 from deforming in those areas not having spacers 152.

Semi-flexible shim plates 200 serve a second function. Shim plate 200acts as a semi-flexible cover to compensate for any imperfections orforeign material that may be present. FIG. 12 illustrates an examplewhere a foreign particle 208 is trapped between shim plate 200 and wafer115. FIG. 12 shows that shim plate 200 is flexible enough to conform tothe presence of foreign particle 208 and not disrupt the evendistribution of pressure applied to the perimeter seal areas of wafer115. A shim plate of glass serves this forgiving purpose. If shim plate200 were a rigid material, such as aluminum or steel, any foreignparticles located anywhere between substrate 100 and wafer 115 couldcause excessive pressure at the particle and insufficient pressure inother areas. This would result in a localized area that is over pressedand a large area that is under pressed. A semi-flexible shim plate 200will flex and only an insignificantly small area around foreign particle208 will arguably be insufficiently pressed.

A preferred alternate embodiment to the press assembly technique of FIG.11 and FIG. 12 will now be described. FIG. 14 illustrates the use ofconformal bag press 201. Once optically transmissive substrate 100 andwafer 115 are assembled together as shown in FIG. 10, the assembly maybe placed in conformal bag 203 of bag press 201 as shown in FIG. 14.Conformal bag 203 may be a rectangular shaped, high temperature nylonbag. At this point, tube 206 extending from vacuum pump 204 is coupledto bag end 209 of conformal bag 203. Vacuum pump 204 may be a foodindustry, commercial quality sealer.

With vacuum pump 204 activated, air is drawn from the inside ofconformal bag 203. As air is drawn from the inside of conformal bag 203,conformal bag 203 closes about substrate 100 and wafer 115. Thecompression forces of conformal bag 203 are applied equally about eachsurface of substrate 100 and wafer 115. Since the force per unit surfacearea is greatest on the large, exposed surfaces of retarder layer 110and backplane 120, retarder layer 110 and backplane 120 move verticallytowards one another substantially while maintaining their original,complementary alignment. As the nickel particles within cross-overmaterial 170 are urged into alignment layers 135, the polyimide materialof alignment layers 135 separates until cross-over material 170 contactsreflective pixel layer 125 and conductive coating 130. This vacuum bagmethod is preferred to the clam shell method because, for example,conformal bag 203 easily adjusts to particles trapped between conformalbag 203 and the assembly of substrate 100 and wafer 115.

With a vacuum drawn into sealed, conformal bag 203, conformal bag 203along with the assembly of substrate 100 and wafer 115 is placed into anoven to cure the adhesive of perimeter seal material 150 and cross-overmaterial 170. Preferably, they remain in the oven at 160 deg. C. for 60minutes. In an alternate embodiment, the air within conformal bag 203 isevacuated and conformal bag 203 is back filled with another gas, such asnitrogen, helium, or argon, to displace any oxygen. This back filled gasis then evacuated by vacuum pump 204 to compress substrate 100 and wafer115 together.

With the adhesives cured and cross-over material 170 in a position tocommunicate the cover glass drive voltage from reflective pixel layer125 of wafer 115 to conductive coating 130 of substrate 100, the cellgaps between the individual display area 155 of wafer 115 and opticallytransmissive substrate 100 may be filled with liquid crystal materialbefore individual display devices 300 (FIG. 28 and FIG. 29) are cut andseparated. This filling process is shown in FIG. 16 and FIG. 17. Theassembly (optically transmissive substrate 100 and wafer 115) may befilled by a vacuum fill method common to filling nematic liquid crystaldisplays. The entire assembly is put in a vacuum chamber 210. Chamber210 is evacuated until the pressure reaches approximately 10⁻¹ Torr. Inconnection with FIGS. 7-9, a perimeter seal application process wasdescribed for placing perimeter seal material 150 including spacers 152around wafer 115. As stated, a perimeter seal adhesive 150 is appliedaround the entire wafer 115 except for evacuation gap port 153 to allowair to escape during the press process. Gap 153 now may be used to allowthe entrance of liquid crystal material in the cell gap between theassemblies.

As shown in FIG. 16, the optically transmissive substrate/wafer assemblyis lowered into bath 215 containing liquid crystal material 220. Theassembly is lowered into the bath 215 until evacuation port 153 contactsliquid crystal bath 215. Chamber 210 is then pressurized to atmosphericpressure with a gas, such as nitrogen, helium, or argon, but preferablyair. As illustrated by way of example in FIG. 8, each of individualdisplay area 155 has a fill port 167 to allow liquid crystal material tobe placed in display area 160 of individual display device 300. Thepressure difference between cell gaps 207 of the individual displaydevices and the ambient, forces liquid crystal material 220 into cellgaps 207 throughout the assembly as illustrate in FIG. 17. Once liquidcrystal material 220 is placed in cell gap 207 of each individualdisplay device 200, the excess liquid crystal material 220 is cleanedoff evacuation port area 153. An ultraviolet cure adhesive then isapplied to evacuation port 153 and cured with ultraviolet light to sealthe assembly.

FIGS. 16 and 17 illustrate a process where liquid crystal material isadded to the assembly prior to separating the assembly into individualdisplay devices 300. The liquid crystal material fill process can alsobe accomplished once the individual display are separated from theassembly. This is discussed in connection with FIGS. 30 to 33. In thiscase, evacuation port 153 is filled with an ultraviolet cured adhesiveand cured following just after the press process.

To produce high quality static as well as dynamic real time color fieldimages on an active pixel matrix, the nematic liquid crystal material220 used in a preferred embodiment should meet several factors. Colorfield sequential operation requires a fast pixel switching time underlow voltage operations. Switching speed is proportional to the square ofthe cell gap. In order to meet the fast switching time required forcolor field sequential operations, cell gap 207 should be on the orderof two microns. This relative thinness is a factor in selecting theproper viscosity for liquid crystal material 220. As another factor, theliquid crystal cell should be capable of rotating the polarization ofreflected light by 90 degrees to obtain bright, high contrastoperations. Thus, the liquid crystal layer performs as a quarter-waveplate in a preferred embodiment.

The viscosity of liquid crystal material 220 should be as low aspossible to achieve fast switching speeds. Moreover, in respect to theabove factors, the birefringence (delta n or Δn) of the liquid crystalmaterial should be approximately 0.1. To achieve low voltage operations,the threshold voltage of liquid crystal material 220 should be low, suchas a dielectric constant anisotropy (delta ε or Δε) on the order of atleast 10. In addition, to avoid undesirable temperature effects at theupper operating range of the micro LCD, the clearing point of liquidcrystal material 220 should be at least 20 deg. C. above the highestoperating temperatures for the micro LCD. One having ordinary skill inthe art of manufacturing liquid crystal material is able to compose amaterial meeting the above factors for liquid crystal material 220.

After the wafer assembly is pressed and sealed, the exterior surface ofoptically transmissive substrate 100 is cleaned, for example, with asolvent. If not already applied, an optical film then may be applied tothe entire surface of transmissive substrate 100. In one embodiment,compensating or retarder film 110 is laminated to the entire surface oftransmissive substrate 100 using a roller-type lamination machine. Thelamination is shown in FIG. 18. Compensating or retarder film 110 isused, in one sense, to compensate for unwanted birefringence in adisplay. The film is used to compensate for residual birefringance inthe black state that results in a darker black. Compensating or retarderfilm thus provides an improved contrast between black and white.

Compensating or retarder film 110 must cover the active area of thedisplay after it is completely assembled. In most display applicationsthat use a compensating or retarder film, the compensating or retarderfilm is laminated to the individual displays after they are separatedfrom the wafer substrate. This is a labor-intensive process for smalldisplays with many displays on a large substrate. The invention teachesa process in which a film, either retarder or polarizer, is laminated tothe glass prior to separating the displays. It is to be appreciated thatcompensating or retarder film 110 can be laminated to each individualdisplay assembly after they are formed and separated.

In street areas 230 between the individual display devices, compensatingor retarder film 110 is then removed, using a laser as shown in FIG. 19.This removal exposes transmissive glass material 102 to allow it to bescribed, for example, using a carbide wheel.

Next, as shown in FIG. 20, in the case where transmissive substrate 100is square, a dicing saw may be used to scribe relative fiducial oralignment marks 240 and 245 on optically transmissive glass substrate100. To scribe marks 240 and 245, the assembly is placed on the vacuumchuck of a dicing saw with patterned-side 117 (see FIG. 2) ofsemiconductor wafer 115 set in the face up position. When the assemblyis mounted on the vacuum chuck to cut wafer 115 (i.e., circuitrypatterned side 117 of wafer 115 is face down) scribe marks 240 and 245in transmissive substrate 100 are visible through glass material 102 andmay be used for alignment. The camera uses alignment or registrationmarks 240 and 245 to cut wafer 115 from the backside, since marks 240and 245 are relative to micro display area 155 of wafer 115.

Next, as shown in FIG. 21, semiconductor wafer 115 is diced from thebackside, which has no patterns visible on wafer 115 to use asregistration marks for the dicing process. FIG. 21 shows the assemblyplaced with optically transmissive substrate 100 face down (i.e.,circuitry patterned side 117 of wafer 115 is “down”) on the vacuumchuck. Scribed alignment marks 240 and 245 on transmissive substrate 100are visible through glass material 102 to aid alignment. The backside ofwafer 115 is then cut according to the patterning registered by thecamera and aligned by registration marks 240 and 245. FIG. 21 shows cut255 in an X-direction and cut 260 in a Y-direction. FIG. 22 shows thebackside of wafer 115 after the subsequent step of partial cutting ofall of semiconductor wafer 115 in an aligned relation to the patterningon the patterned side of wafer 115, using registration marks 240 and 245as an aid, so that the assembly may be divided or “singulated” intoindividual display 300. Wafer 115 is partially cut using a water-cooledwafer dicing saw. The depth of the saw blade is set to cut partiallythrough the thickness of wafer 115, in one embodiment, removing enoughmaterial to easily divide wafer 115 in a later process, but retainingenough material to prevent water from entering cell gap 207 (FIG. 11)between wafer 115 and transmissive substrate 100. Wafer 115 is then cutin a wet-sawing process. After the partial cutting, wafer 115 isthoroughly dried.

Optically transmissive glass substrate 100 provides support forsemiconductor wafer 115 during the cutting, drying, and handlingprocesses. In addition, optically transmissive substrate 100 preventswafer 115 from flexing and possibly breaking at the cuts which wouldallow water to enter the gap between the substrates. Because of thesupport provided by transmissive substrate 100, the depth of the saw cutcan be very close to the thickness of wafer 115 without significant riskof water leakage, for example, approximately 80% of the thickness ofwafer 115 can be cut.

Because no patterns are visible on the backside of semiconductor wafer115, an alternative process to the process described above withreference to FIGS. 21 and 22 is to mount the programmable camera beneaththe dicing saw. Thus, wafer 115 is placed on the vacuum chuck andaligned to a camera mounted under the vacuum chuck. A marking devicewith X-Y motion capabilities, such as a laser or carbide needle,contacts the backside of wafer 115 and creates two registration marks onthe patterned surface of wafer 115. The registration marks are then usedin the cutting process.

After the cutting process and the assembly drying process, a dry cuttingprocess is used to scribe transmissive substrate 100. In the embodimentwhere optically transmissive substrate 100 is glass material 102, theglass must be scribed using a dry process because, after it is scribed,the assembly has no support to prevent the glass or wafer 115 fromcracking. Cracks in either substrate would allow any liquid used in theprocess to enter cell gap 207 between the substrates, i.e., cell gap 207where liquid crystal material exists or is to be placed.

To scribe optically transmissive substrate 100 in the embodiment wherematerial 102 is a glass substrate, the assembly is placed withpattern-side 117 of wafer 115 facing n the up direction (opticallytransmissive substrate 100 side “up”) on the vacuum chuck of a carbidewheel type glass scribing machine such as that manufactured by VillaPrecision International. The glass is scribed with the carbide scribewheel in the locations where the glass will separate, e.g., directlyaligned or in an aligned relation with the scribe areas of wafer 115.The glass can also be cut with a laser process. FIG. 23 shows theassembly after the scribing of glass material 102 in an X-direction.Scribing 248 is located in those areas where optically transmissivesubstrate will separate. In an X-direction, in this embodiment, scribing248 is in an aligned relation to scribe areas 265 of wafer 115.

FIG. 24 shows the assembly after the scribing of glass material 102 in aY-direction. In a Y-direction, glass material 102 is not scribeddirectly over scribe areas of wafer 115. Instead, scribing 250 isslightly offset. The offsetting serves to expose a portion of wafer 115as offset portion 119 for each eventual display. The exposure of offsetportion 119 of wafer 115 is done to allow a subsequent step of making anelectrical connection to the individual display when the display ispackaged. Offset portion 119 is best seen in FIG. 35 and FIG. 36.Exposed area 119 of the individual display may have bond pads 405 orother contacts coupled to the circuit devices of the individual displayas seen in FIG. 36.

FIG. 25 shows a top view of the assembly with pattern-side 117 of wafer115 facing in the up position (optically transmissive substrate 100 side“up”). FIG. 25 shows transmissive substrate 100 scribed in areas wheretransmissive substrate is to be separated, i.e., scribing 248 in anX-direction directly aligned with or in an aligned relation with thescribe areas of wafer 115 and scribing 250 in a Y-direction offset fromthe corresponding Y-axis scribe areas of wafer 115.

After transmissive substrate 100 is scribed, scribe marks 248 and 250are “vented.” Venting is the process by which optically transmissivesubstrate 100, such as a glass, is cracked at the location of the scribeso as to directionally propagate the crack through the thickness ofglass substrate 100. The venting can be accomplished either manually orusing an automated machine process.

A singulation process embodiment preferred over the square glasssingulation process described in connection with FIGS. 18 through FIG.25 will now be described. FIG. 26 shows an embodiment where theperimeter of transmissive substrate 100 follows the generally roundperimeter of wafer 115. Since the perimeter of transmissive substrate100 follows the round perimeter of wafer 115, the same equipment used tohandle wafer 115 may be used to handle substrate 100.

As shown in FIG. 26, wafer 115 with round glass substrate 100 is mountedto a vacuum chuck with pattern-side 117 of wafer 115 facing in the updirection. Material is removed from substrate 100 in the X-direction toreveal top exposed wafer 270 and X-surface substrate 272 and in theY-direction to reveal side exposed wafer 274 and Y-surface substrate 276as shown. As shown in FIG. 27, at top exposed wafer 270, material isremoved from wafer 115 parallel to X-surface substrate 272 to formX-registration 278. At side exposed wafer 274, material is removed fromwafer 115 parallel to Y-surface substrate 276 to form Y-registration280.

With X-registration 278 and Y-registration 280 machined into wafer 115,wafer 115 is flipped over so that pattern-side 117 is facing down. Now,cuts similar to those shown in FIG. 21 and FIG. 22 may be made intobackplane 120 using the relative registration provided by X-registration278 and Y-registration 280. Transmissive substrate 100 may now bescribed and vented as discussed in connection with FIGS. 23, 24, and 25.

This round glass method is preferred since it eliminates the extrahandling tools needed to handle a square piece of glass. This isespecially acute when the diameter of wafer 115 is 8.0 inches. There,the diagonal of a square piece of glass exceeds 11.3 inches—a length inwhich most existing equipment in this area is not capable of handling.

Once transmissive substrate 100 is vented, the remaining siliconmaterial at the scribe locations unifying wafer 115 can be easily brokenand the individual display assemblies separated as shown in FIGS. 28 and29. FIG. 28 shows the separated individual display assemblies 300 froman X-direction and FIG. 29 shows the same assemblies 300 from aY-direction.

An alternative to the above assembly, cutting, scribing, and ventingprocess is to divide the substrates individually. For example, wafer 115can be cut into individual device, then assembled to an individualtransmissive substrate panel of substrate 100. In this manner, thescribe marks on wafer 115 can be used to cut wafer 115 into theindividual display device from the top (i.e., circuitry patterned-side117 facing up). Optically transmissive substrate 100 components can thenbe properly aligned and coupled to wafer 115 in a process similar tothat described above with coupling substrate 100 to wafer 115. A thirdalternative is to assemble a similarly sized transmissive substrate 100to wafer 115 prior to dividing the assembly into individual displaydevices 300. In this embodiment, concerns over cutting wafer 115 fromthe non-patterned side are addressed by mounting the camera below thedicing saw to align the cuts to the scribe marks on the patterned sideof wafer 115.

Once the individual display devices 300 are separated from the wafer,they are either filled with liquid crystal material or, if alreadyfilled, sealed at their fill ports to retain liquid crystal material 220in cell gap 207. Recall that in FIG. 8 and the accompanying text,perimeter seal material 150 surrounded the wafer to define eachindividual display device or assembly and fill port 167 was left toallow the placement of liquid crystal material 220 in display area 160.Where liquid crystal material 220 is located in cell gap 207 of displayarea 160 of device 300, fill port 167 is filled by the application of anultraviolet cure adhesive that is cured with an ultraviolet light.

FIGS. 30 and 31 illustrate the situation where the individual displaydevices 300 have not been previously filled with liquid crystal material220. In FIG. 30, singulated device 300 is put in vacuum chamber 315.Chamber 315 then is evacuated until the pressure reaches 10⁻¹ Torr.Display device 300 is lowered so that the end of device 300 having fillport 307 contacts liquid crystal material 310 in bath 305. Fill port 307may be of fill port 167 shown in FIG. 8. Chamber 315 is pressurized withair to atmospheric pressure and the pressure difference between cell gap207 (FIG. 11) and the ambient pressure forces liquid crystal material310 into display area 160 as shown in FIG. 31. Once the individualdisplay device 300 is filled with liquid crystal material 310, theexcess liquid crystal is cleaned off fill port area 307 and anultraviolet cure adhesive is applied to fill port 307. The adhesive isthen cured with ultraviolet light to seal display area 160 of displaydevice 300.

An singulated fill embodiment preferred to that described in connectionwith FIG. 32 and FIG. 33 will now be described. FIG. 32 shows singulateddevice 300 position with fill port 307 facing up within chamber 315.First, air is vacuumed from chamber 315. Then, a drop of liquid crystalmaterial 310 is placed over fill port 307 by dropper 301. Dropper 301 ispreferably in the shape of a short, sturdy, little tea pot having aspout and a handle. With perimeter seal area generally spanning one-halfinches and fill port 207 generally spanning two microns, surface tensionholds liquid crystal material drop 311 in place.

With drop 311 in place, chamber 315 is pressurized. FIG. 33 illustrateschamber 315 in the pressurized state. As chamber 315 is pressurized, thepressure within viewing area 160 is less than the pressure in theremaining area of chamber 315. Due to this pressure difference, liquidcrystal material drop 311 is forced into viewing area 160 as assisted bygravity. Excessive liquid crystal material 311 is cleaned off. Fill port307 is then plugged with ultraviolet cure adhesive and this adhesive isthen cured with an ultraviolet light.

FIG. 34 illustrates a cross-section of individual display 300 from anX-direction, whereas FIG. 35 shows the same assembly from a Y-direction.FIGS. 34 and 35 show liquid crystal material 310 positioned in cell gap207 between optically transmissive substrate 100 and wafer 115.

FIG. 36 shows micro liquid crystal display 400 in a state where microliquid crystal display 400 is ready to be packaged into a micro liquidcrystal display panel. First, overhang 330 of substrate 100 shown inFIG. 35 is removed by, for example, applying a scribe or laser to theglass overhang of display 300. Then, the material comprising alignmentlayer 135 disposed in offset portion 119 is removed to expose land pads405 and other electrical components located in that area. Alternatively,this area may have been masked or alignment layer 135 may be retainedonly to be pierced using a push through technique. Land pads areelectrical contact pads that permit electrical communication between thecircuitry within micro liquid crystal display 400 and devices externalto micro liquid crystal display 400 such as a device driver located on adriver board. Micro liquid crystal display 400 may then be enclosedwithin an anti-static bag and packaged for shipment with other displays400 in a box or some other convenient shipping container.

Micro liquid crystal display 400 may be integrated with other existingcomponents. For example, FIG. 37 shows single-chip radio 500manufactured by Lucent Technologies Inc. in Allentown, Pa. in itsMicroelectronics Group. Single-chip radio 500 may be thought of as alow-power, tiny radio/microphone made of aluminum nitride on a siliconsurface and built by using silicon micromachining and etching materialfrom a silicon integrated circuit such as wafer 115. As a radio,single-ship radio 500 works towards communicating audible signalsthrough wireless transmission as encoded in electromagnetic waves,preferably in the approximate frequency range from 10 kilohertz to300,000 megahertz. As a microphone, single-ship radio 500 works towardsconverting sound waves into an electric current that may be fed into anamplifier, a recorder, or a broadcast transmitter.

As shown in FIG. 37, base 510 of single-chip radio 500 measuresapproximately 600 microns (0.6 millimeters) in length. Give its smallsize and construction out of wafer material, single-chip radio 500 maybe integrated into wafer 115 and disposed in convenient locations 503along offset portion 119 indicated in FIG. 36. The perimeter of wafer115 may also be extended out beyond the footprint of substrate 100 inany direction to provide more convenient locations 503. The integrationof single-chip radio 500 of FIG. 37 into micro liquid crystal display400 permits building miniature portable devices such as head mounteddisplay products or telephone watches that will use voice recognitionthrough single-chip radio 500 and have static and dynamic, real timevideo capabilities through viewing or display area 160.

An essential part of single-chip radio 500 for use in miniature portabledevices is small radio frequency (RF) filter 520 illustrated in FIG. 38.RF filter 520 is a component that shields unwanted radio frequencies andis manufactured by Lucent Technologies Inc. in its MicroelectronicsGroup. For any instrument that both converts sound signals into a formthat can be transmitted to remote locations and receives and reconvertswaves into sound signals, an RF filter is used to protect the receiveron the instrument from the transmitter on the instrument. Inconventional cell phones for example, the RF filter, made of a ceramicmaterial, is by far the largest single component. FIG. 38 illustrates asize comparison between U.S. penny 522, conventional ceramic filter 524,and miniature RF filter 520.

FIG. 39 shows a tank circuit 530 also built by Lucent Technologies Inc.using silicon micromachining techniques. Tank circuit 530 includesinductor 534. Inductor 534 is a simple loop of wire that helps determinethe proper frequency for communications in a miniature portable device.Inductor 534 is shown warped away from silicon surface 536 in the shapeof a taco shell. First flat plate 540 and second flat 542 comprisecapacitor 548. With capacitor 548 storing an electric charge, inductor534 and capacitor 548 together determine a frequency that is proper forcommunications telephone watches. For tank circuit 530, the frequencymay be established at the 1960 MHz required to communicate using theworldwide cellular PCS network.

In the preceding detailed description, the invention is described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader scope of subject matter as set out in theclaim terms. The written and drawing specification is, accordingly, tobe regarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. A liquid crystal display assembly, comprising: afirst substrate having an optically transmissive character; a secondsubstrate having a reflective character, the second substrate positionedadjacent to the first substrate and having a plurality of active areaswherein each of the plurality of active areas are bordered by aperimeter seal area; a plurality of spacers configured about eachperimeter seal area of the second substrate, wherein the first substrateis separated from the second substrate by the plurality of spacers so asto form a plurality of gaps; and a liquid crystal material positionedbetween the first substrate and the second substrate within each gap,and wherein each of the plurality of spacers are restricted to alocation that is outside of each of the plurality of active areas, andthe second substrate having a perimeter, the first substrate having aglass cover, the glass cover having a perimeter that substantiallyfollows the perimeter of the second substrate, and wherein the perimeterof the glass cover is circular and falls within an eight inch diameter.2. The liquid crystal display assembly of claim 1 wherein the perimeterof the glass cover comprises at least one straight portion.